1. Field of the Invention
The neon lamp is a known illumination device formed of an evacuated glass tube confining an ionizable gas and a small amount of mercury, electron emitting cathodes, and having electrical terminals at each end. Upon application of the proper electrical voltage to the terminals, the gas becomes ionized and an electrical arc is established between the cathodes through the gas inside the tube, evidenced by the arc. Neon lamps emit different colors of light, according to the composition of the gas. Neon lamps find wide usage for advertising and display purposes because of the colorful illumination provided by the ionized neon gas.
As is known, the neon lamp is a peculiar type of electrical load which possesses a "negative resistance". That is, a given high voltage is required to start the lamp and, once started, a lesser voltage is required to sustain its operation.
Until the present, the only apparatus used in powering neon lamps is one which steps up the line voltage, to the higher starting voltage, by means of a bulky step-up transformer of the high leakage reactance type, in which the secondary winding is connected across the lamp to provide the high starting voltage and, once the lamp ignites, to limit current to "ballast" the lamp. This step-up transformer is fed directly by the low frequency line carrying commercial alternating current as provided by public utility companies. Commercially available power is normally provided at a frequency between 50 hertz to 60 hertz and a voltage between 110 to 120 volts.
Like any electro-magnetic device, a conventional transformer used to operate neon lamps is inherently noisy when operated from an alternating current of 60 hertz. The amount of noise varies to a degree dependent upon the size of the transformer, and the deterioration rate of the varnishes and insulator materials. The reason for the noise is that lamp voltage waveforms contain harmonic components ranging from 120 hertz up to 3,600 hertz and even higher. Therefore, the noise generated by conventional transformer systems for driving neon lamps varies from a low pitched hum to a high pitched "rustle". In conventional transformers noise is generated by vibration of the laminated transformer core and by stray magnetic fields which cause vibration of the transformer case or even the frame in which the transformer is mounted.
One further disadvantage of conventional neon lamp transformers is the large volume and weight of such devices. Because a neon lamp requires a very high starting voltage and a high operating voltage, the ballast impedance required to stabilize the negative impedance of this type of lamp is accomplished with a leakage reactance transformer. Such transformers are quite large and bulky, and frequently must be located some distance from the lamp frame. Also increasing the volume of this type of transformer is the high dielectric resistance material needed between the layers in the secondary winding because of the high voltage present.
Another disadvantage in the conventional neon lamp transformers is the I.sup.2 R loss in the copper wires. This loss, as its name implies, is equal to the sum of the squares of the currents multiplied by the resistance of the various windings. As the currents are fixed by the rating, it is evidently impossible to reduce the values in order to reduce the I.sup.2 R losses. In a conventional transformer, for example, to feed a load of 15,000 volts of neon lamps, the resistance in the secondary winding is about 18 K-ohms, and the current 0.028 Amps. Thus, the losses in the copper wire are I.sup.2 R=18,000.times.0.028.sup.2 =14 Watts.
One further loss is caused by the eddy currents in individual conductors which are set up by stray magnetic fields. The loss in these fields is directly proportional to the leakage fields and to the total weight of copper, two characteristics of this type of transformer.
Another important loss is the hysteresis loss in core plates. This loss is dependent upon the material of the core plates used and is proportional to the weight of material used. A heavy weight core is an inherent characteristic of this type of transformer.
The last important loss is the eddy current loss in core plates, also directly proportional to the volume of the core.
Important in sign display is animation, through intermittent flashing of sections of the lamps to attract attention. With the conventional transformer to operate neon lamps there are two ways to accomplish flashing. One of them is low voltage flashing and is accomplished in the primary circuit of the high voltage transformer. The other one is secondary flashing and is accomplished in the secondary circuit of the high voltage transformer.
In low voltage flashing, the contacts of the device used to accomplish that effect must handle all the current of the transformer, normally ranging from 2 Amps to more than 13 Amps, depending on the rated load of the transformers. This high current produces sparks between contacts, leading to short contact life and high maintenance cost. It also may result in faulty flashing as evidenced by the irregular operation of the flasher and may be accompanied by heavy arcing and radio interference.
The secondary flasher, on the other hand, has the disadvantages of requiring long high voltage cables from the flasher to each section of tubing and the difficulty of maintaining a high voltage flasher in good repair because of the high voltage arcing between the contacts.